(a) Field of the Invention
The present invention relates to a method for preparing cerium oxide, cerium oxide prepared therefrom and CMP slurry comprising the same. More specifically, the present invention relates to a method for preparing cerium oxide which enables preparation of cerium oxide showing improved polishing performance, cerium oxide prepared therefrom, and CMP slurry comprising the same.
(b) Description of the Related Art
In recent years, a semiconductor manufacture process shows a tendency to increase a diameter of wafer, and severe manufacture environments such as decrease in minimum line width required for device manufacture to 0.13 μm or less, is required for ULSI (Ultra Large Scale Integration). And, for improvement in device performance, a process of forming multiple interconnection or multilayer interconnection on a wafer is essentially required. However, non-planarization of a wafer generated after the above process may decrease subsequent process margin or deteriorate device property. In order to overcome these problems, planarization techniques are used for various manufacture processes.
As the planarization technique, CMP (chemical mechanical polishing) is predominantly used, which presses the surface of a polishing pad that rotates relatively to a wafer surface with providing CMP slurry to the polishing pad, thereby planarizing the wafer surface by chemical and mechanical operations.
The CMP technique can be used in the step of polishing a silicon oxide layer until a polishing stop layer, e.g., a silicon nitride layer is exposed, after the silicon oxide layer is deposited so as to embed a trench on a wafer, during the process of forming a device isolation layer by STI (shallow trench isolation).
Wherein, it is more preferable that removal selectivity for a silicon oxide layer compared to a silicon nitride layer (a silicon oxide layer polishing rate compared to a silicon nitride layer polishing rate) is higher. If the removal selectivity for the silicon oxide layer compared to the silicon nitride layer is low, it is difficult to uniformly remove a pattern of a polishing stop layer such as the silicon nitride layer, and thickness change of the polishing stop layer may be large over the whole wafer. Thus, a level difference between an active area and a field area may be caused in the final structure having a trench to decrease subsequent process margin, thus decreasing economical efficiency.
CMP slurry generally comprises an abrasive, a dispersant and water. And, physicochemical property of the abrasive influences on polishing performance such as a silicon nitride layer polishing rate, a silicon oxide layer polishing rate, removal selectivity for a silicon oxide layer compared to a silicon nitride layer, etc.
Particularly, strength or size of an abrasive is closely related to polishing rate of the surface to be polished. The abrasive can polish the surface to be polished by a mechanical polishing device. And, the higher strength and the larger size of the abrasive increase the silicon nitride layer or silicon oxide layer polishing rate.
Meanwhile, in case cerium oxide is used as an abrasive, cerium oxide is known to be capable of chemical polishing in addition to mechanical polishing. Cerium oxide can form a chemical bond of Si—O—Ce due to its high reactivity with a silicon oxide layer, thereby removing silicon oxide mass on the surface of a silicon oxide layer to polish the silicon oxide layer. Removal selectivity for the silicon oxide layer compared to the silicon nitride layer, especially a silicon oxide layer polishing rate can be varied according to chemical activity of cerium oxide.
Accordingly, it is required to appropriately control physicochemical properties of cerium oxide used as an abrasive in order to increase circuit reliability and improve economical efficiency of manufacture.